The use of heat pumps for space heating of air is well known. One conventional type of heat pump, the air to air heat pump, normally draws heat from the air outside an enclosure and uses it to upgrade the temperature of air within the enclosure. It is appreciated that the operating coefficient and thus the efficiency of the heat pump is a positive function of the temperature of the heat supplying medium, i.e. the outside air.
The use of phase-change materials as a heat-storage medium has been proposed in the literature. An example of a heat-storage system using phase-change materials is described in applicant's pending Israel Patent Application Ser. No. 62355.